linux-kernel - Re: [PATCH v2 10/16] x86: probe assembler capabilities via kconfig instead of makefile

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Date:   Thu, 26 Mar 2020 10:49:35 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/16] x86: probe assembler capabilities via kconfig
 instead of makefile

On Thu, Mar 26, 2020 at 1:02 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> From: "Jason A. Donenfeld" <Jason@...c4.com>
>
> Doing this probing inside of the Makefiles means we have a maze of
> ifdefs inside the source code and child Makefiles that need to make
> proper decisions on this too. Instead, we do it at Kconfig time, like
> many other compiler and assembler options, which allows us to set up the
> dependencies normally for full compilation units. In the process, the
> ADX test changes to use %eax instead of %r10 so that it's valid in both
> 32-bit and 64-bit mode.

Does KConfig generate -D<foo> flags for KBUILD_CFLAGS and KBUILD_AFLAGS?
Looks like lib/raid6/test/Makefile also generates some of these?

>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
> Changes in v2: None
>
>  arch/x86/Kconfig           |  2 ++
>  arch/x86/Kconfig.assembler | 17 +++++++++++++++++
>  arch/x86/Makefile          | 10 ----------
>  3 files changed, 19 insertions(+), 10 deletions(-)
>  create mode 100644 arch/x86/Kconfig.assembler
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index beea77046f9b..707673227837 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2935,3 +2935,5 @@ config HAVE_ATOMIC_IOMAP
>  source "drivers/firmware/Kconfig"
>
>  source "arch/x86/kvm/Kconfig"
> +
> +source "arch/x86/Kconfig.assembler"
> diff --git a/arch/x86/Kconfig.assembler b/arch/x86/Kconfig.assembler
> new file mode 100644
> index 000000000000..91230bf11a14
> --- /dev/null
> +++ b/arch/x86/Kconfig.assembler
> @@ -0,0 +1,17 @@
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2020 Jason A. Donenfeld <Jason@...c4.com>. All Rights Reserved.
> +
> +config AS_AVX2
> +       def_bool $(as-instr,vpbroadcastb %xmm0$(comma)%ymm1)
> +
> +config AS_AVX512
> +       def_bool $(as-instr,vpmovm2b %k1$(comma)%zmm5)
> +
> +config AS_SHA1_NI
> +       def_bool $(as-instr,sha1msg1 %xmm0$(comma)%xmm1)
> +
> +config AS_SHA256_NI
> +       def_bool $(as-instr,sha256msg1 %xmm0$(comma)%xmm1)
> +
> +config AS_ADX
> +       def_bool $(as-instr,adox %eax$(comma)%eax)
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index f32ef7b8d5ca..b65ec63c7db7 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -177,16 +177,6 @@ ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
>         KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
>  endif
>
> -# does binutils support specific instructions?
> -avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)
> -avx512_instr :=$(call as-instr,vpmovm2b %k1$(comma)%zmm5,-DCONFIG_AS_AVX512=1)
> -sha1_ni_instr :=$(call as-instr,sha1msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA1_NI=1)
> -sha256_ni_instr :=$(call as-instr,sha256msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA256_NI=1)
> -adx_instr := $(call as-instr,adox %r10$(comma)%r10,-DCONFIG_AS_ADX=1)
> -
> -KBUILD_AFLAGS += $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr) $(adx_instr)
> -KBUILD_CFLAGS += $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr) $(adx_instr)
> -
>  KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
>
>  #
> --
> 2.17.1
>


-- 
Thanks,
~Nick Desaulniers